A liquid-cooled device, such as an engine or similar heat-producing device, must operate within specified temperature limits for two basic reasons: (1) if the engine operates at temperatures that are too low, inefficient operation and possible engine damage will result, and the engine may not respond properly to load changes; an example is the case of trying to accelerate an automobile rapidly when entering freeway traffic and the engine is cold; and (2) if the engine operates at temperatures that are too high, the engine will be damaged and will stop running due to differences of expansion of the various engine parts causing mechanical interferences and binding; an example is the case of an automobile engine stopping soon after its coolant is lost.